NASA space transportation plans and roles of a mixed fleet

An account is given of the results of a September, 1987 NASA 'mixed fleet' launching resources/scheduling study that predicated capability projections on a fleet of available ELVs. The launch capability projections extended as far as 1995, and in their later phases encompassed the resumption of Space Shuttle operations and the availability of Orbital Maneuvering Vehicle, which could accomplish such things as the reboosting of the Hubble Space Telescope in 1991, and even the Shuttle-Derived Vehicle, of which two distinct concepts are presently being considered; both would heavily rely on Space Shuttle hardware, but would be unmanned.